Abstract
Migratory decisions in birds are closely tied to environmental cues and fat stores, but it remains unknown if the same variables trigger bat migration. To learn more about the rare phenomenon of bat migration, we studied departure decisions of female common noctules (Nyctalus noctula) in southern Germany. We did not find the fattening period that modulates departure decisions in birds. Female noctules departed after a regular evening foraging session, uniformly heading northeast. As the day of year increased, migratory decisions were based on the interactions among wind speed, wind direction and air pressure. As the migration season progressed, bats were likely to migrate on nights with higher air pressure and faster tail winds in the direction of travel, and also show high probability of migration on low-pressure nights with slow head winds. Common noctules thus monitor complex environmental conditions to find the optimal migration night.
Highlights
Migration is a fascinating animal behaviour, and yet we still lack the most basic information, especially from non-model organisms [1,2,3]
A predictive model like the one we present here, based on data from a multi-year telemetry study on the common noctule (Nyctalus noctula), can provide useful insights to target tracking periods and for wind power planning [7,8]
The best performing environmental models included increasing numerical day of year and several iterations of the interactions of wind direction, wind speed, and air pressure. As these factors interacted across the migration period, bats were more likely to migrate on nights with faster tail winds, beginning at the median wind speed of 2 m s21, on nights with higher air pressure
Summary
Migration is a fascinating animal behaviour, and yet we still lack the most basic information, especially from non-model organisms [1,2,3]. While over 30% of Palaearctic and Antarctic birds migrate long distances [4], only a few of the more than 1300 bat species have maximum migration distances of over 1000 km [5,6]. In European temperate bats, females primarily execute long-distance northeasterly migrations to insect-rich regions [6,8]. After hibernation, they begin gestation and are under considerable time pressure to raise offspring having travelled hundreds of kilometres to the same maternity colony each year. Bats should time their migration departure to take advantage of environmental conditions [10] conducive to long flights (i.e. over 100 km, [11]) and arrive at maternity colonies when insect abundance begins to rise
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